Merge pull request #415 from smallstep/jeff/typo

Add missing word ("is")

Author: tashian

platform/README.mdx

@@ -110,7 +110,7 @@ Talk to Smallstep’s Customer Engineering Team at [support.smallstep.com](http:
 
 ## Smallstep Open-Source Toolchain
 
-Our open source toolchain the most popular open-source certificate management toolchain, and was designed for DevOps and homelab or POC use cases. However, it’s not a device identity platform, and doesn’t solve the problems listed above out-of-the-box.
+Our open source toolchain is the most popular open-source certificate management toolchain, and was designed for DevOps and homelab or POC use cases. However, it’s not a device identity platform, and doesn’t solve the problems listed above out-of-the-box.
 
 Our open-source toolchain provides IT/Security/DevOps engineers with an extensive internal PKI toolchain, which includes everything needed to automate the deployment and management (renewal, revocation, and monitoring) of certificates for a broad range of contexts, use cases, and environments.